Titanium cutting tools with high binder phase content

ABSTRACT

THIS PATENT DESCRIBES NOVEL TITANIUM CARBIDE CUTTING TOOL COMPOSITIONS WITH A HIGH BINDER PHASE CONTENT COMPRISING THE INTERMETALLIC COMPOUNDS MONI OR MO6CO7, SAID COMPOSITION CONTAINING FROM ABOUT 13.6% TO ABOUT 30% BY WEIGHT MO.

s. WINDISCH 3,764,275

TITANIUM CUTTING TOOLS WITH HIGH'BINDER PHASE CCNTENT Oct. 9, 1973 Filed July 29. 1970 Em 2 323 E; 9 22:3 32:. I o C 0.82 2 22:31: oz :50

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US. Cl. 29-2823 3,764,275 Patented Oct. 9, 1973 3,764,275 TITANIUM CUTTING TOOLS WITH HIGH BINDER PHASE CONTENT Windisch, Vienna, Austria, assignor to Aerojet- General Corporation, El Monte, Calif. Filed July 29, 1970, Ser. No. 59,062 Int. Cl. B2215 3/12 Stefan 4 Claims ABSTRACT OF THE DISCLOSURE This patent describes novel titanium carbide cutting tool compositions with a high binder phase content comprising the intermetallic compounds MoNi or M 00 said composition containing from about 13.6% to about 30% by weight Mo.

BACKGROUND OF THE INVENTION Titanium carbide has for many years been a main constituent in many alloys used for cutting tools. However, titanium carbide has never achieved as wide a usage as tungsten car-bide although the latter is less hard and more expensive than titanium carbide. There are two main reasons which explain the preferential use of tungsten carbide. One has been due to the greater tendency of titanium carbide to be contaminated by oxygen. The second factor is that the same relative weight percent (3-18%) of binders (typically cobalt), which are used in tungsten carbide tools, have been utilized in the fabrication of titanium carbide tooling without regard for the great difierence in atomic weights between tungsten and titanium. On a chemical basis, titanium carbide can tolerate and even necessitates a much greater amount of binder phase (expressed in moles or atomic percentage) than indicated by the comparative 3 to 18 wt. percent used with tungsten carbide. The relatively lower amount of binder used with the titanium carbide cutting tools, then, may explain the lack of optimization of some of their physical properties.

More recently, there has been developed a composition intended for use in the fabrication of cutting tools containing titanium carbide and a molybdenum-containing binding alloy consisting essentially of 25-75% molybdenum, molybdenum carbide, and mixtures thereof and an alloying metal which is iron, cobalt, nickel or alloys thereof, the total molybdenum content of the composition not exceeding 13% by weight and the binding alloy comprising -50% by weight of the composition. This composition is described in greater detail in US. Reissue Pat. No. 25,815. The present invention, by way of contrast, contains over 13.6% by weight molybdenum which has been found to provide many unexpected results, as is more fully hereinafter illustrated.

SUMMARY OF THE INVENTION Briefly, the present invention comprises novel titanium carbide cutting tool compositions with a high content of binder phase comprising the intermetallic compounds MoNi or Mo co said composition containing from about 13.6% to about 30% by weight M0. The total molybdenum-l-cobalt or nickel content comprises about 25 to 50 wt. percent of the final cutting tool alloy. The present invention further includes a novel method of preparing a novel titanium carbide composition which comprises combining titanium carbide with a preprepared alloy selected from the group consisting of MoNi and MOgCOq, forming the mixture and thereafter sintering the mixture at elevated temperatures to form a novel cutting tool composition containing at least 13.6% by weight Mo.

It is an object of the present invention to provide a novel titanium carbide composition suitable for the fabrication of cutting alloys.

More specifically, it is an object of the present invention to provide a novel titanium carbide composition suitable for cutting tools and containing a high content of binder phase.

Still another object of the present invention is to overcome the problems previously associated with titanium carbide cutting tool compositions.

These 'and other objects and advantages of this invention will ;be apparent from the more detailed description which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS The final product of this invention contains fine TiC- carbide grains, partly connected epitacticly with MoC, cemented by a tough Ni or C0 alloy which has dissolved Mo within the alloys solubility limits.

Cutting alloys made from TiC with about 25 to 50 wt. percent MoNi are preferably sintered at about 1490 C. to 1530'C., and more preferably at about 1500 C. Cutting alloys made from TiC and about 25-50 wt. percent MOsCOq are preferably sintered at 1610 C. Both compositions are tested on stainless steel AISI 347 (hardened to BHN 149-156). Their performance indicates that the very hard TiC (+MoC) and the tough Ni(Mo) or Co(Mo)-alloy binder results in a tool for wide applicability.

The principal contribution of this invention is 'a carbide cutting tool with lower wear in performing medium and fine cuts. The use of the intermetallic compounds MoNi or Mo co results in the ability of varying physical properties (hardness, flexure strength) by changing the sintering duration (1 to 6 times a minimum sintering time) and by composition (1 TiC+0.137 to 0.33 binder phase, data in mol percent):

This invention is believed to involve the peritectic decomposition of the intermetallic compounds MoNi or MOsCOq followed by subsequent reaction with TiC according to the following reaction equations:

(Limits not yet established) temperature it decomposes peritecticly, forming a nickelmolybdenum melt and a solid phase of molybdenum. The molybdenum dissolved in the melt reacts with TiC forming an epitactic MoC on the TiC grains. By this reaction the molybdenum loss in the melt is replaced by additional molybdenum dissolving into the melt from the still solid phase until all molybdenum is converted into MoC. This reaction is preferably performed between 1490 and 1530 C. The sintering temperature should be kept close to 1500 C. Temperatures 1470 C., lead to tool bits which have the metal phase in its original state; i.e., the molybdenum does not yet or only slightly react with TiC. Tool bits prepared in this manner have properties approaching those of the compositions described in the above-identified reissue patent. 0n the other hand, if the temperature approaches 1550 0, rapid grain growth occurs, and a solid solution of (Ti, Mo)C is formed.

The M0 00 compound is stable up to about 1500 C.

and also decomposes peritectically. The utilization of The above considerations are shown by the results of the cutting tests (Table 1 and FIG. 1).-Some alloys were sintered for various durations (16 to 100 min.) at 1490 or 1500 C. Other specimens were sintered in the range 1440 to 1470" C. Seven samples sintered at 1500 C. were compared with five specimens sintered at 1440 and 1470 C. and with commercial tools.

Under the chosen conditions, commercial toolsshow a wear land of 0.016 inch (arbitrary industrial test end point) after 40 to 50 min. Tools of this invention sintered at 1500 C. had a wear land of 0.007 in. after this duration. One of these tools was used for 90 min; the wear was 0.008 inch. The tools sintered at 1440 to 1470" C. had a high wear-in (0.005 after 2 min.) and were not further tested.

TiC-powder is preferably ball milled together with above-mentioned intermetallie compounds (duration depends on the size and speed of ball mill), and the cold pressed pieces sintered in hydrogen atmosphere.

The sinter duration for V2 by /2 inch tool bits can be varied between 16 min. to 100 min. at 1500 C.; the long time sintered alloys are more brittle than the short time 0.010 inch/rev., depth of cut: 0.050 inch. The to ol bit "I was tested at.a depth of cut of 0.125 inch and increasing sintered ones because more M0 is converted into the hard MoC-phase. Besides the sintering duration, the ratio of TiC to intermetallic compound was also varied. Alloys containing from to 50 wt. percent MoNi (or MogCo can be prepared by this method.

Conventional carbide tools with a high content of TiC are recognized under the microscope of their round grains. This results from detrimental grain growth during sintering. I have found that the MoNi (or Mo Co )-compound which is used in this invention decomposes peritecticly. When melting occurs, the molybdenum reacts with TiC; there are numerous nuclei present for formation of Mo-carbide. According to this invention, the grain growth of TiC is minor compared with present TiC alloys. Furthermore, there is the possibility of influencing the hardness and ductility of alloys of this invention. It was found that the tool bits (size ,-in. by .&-in.) were dense after 16 min. at 1500" C. Increasing the sintering time up to 100 min. did not cause grain growth, but converted more molybdenum into Mo-carbide by lowering the carbon content of the relatively broad TiC-phase. This results in harder, more brittle alloys; this property-sintering time dependency permits one composition to be used for a wider range of applications.

The following example is presented solely to illustrate the invention and should not be regarded as limiting in any way. In the example, the parts and percentages are by weight unless otherwise indicated.

EXAMPLE TiC-powder was ball milled for one week together with pre-alloyed MoNi or M05007. A camphor in ether solution was added as pressing aid. A cold pressed bar was cut into square-shaped pieces, yielding bits slightly larger than %-in. by Vz-in. Dewaxing and sintering was done in one pass in one furnace, all under hydrogen. The most favorable sintering condition for tool bits of the above mentioned size with MoNi-binder is 1500 C., while for alloys with Mo co -binder, the temperature is 1610 C. For the cutting test, the tool bits have to be polished on both faces.

In the following table, samples, sintering conditions, and results of the cutting tests are show. The stock metal 'bar was A181 347 (annealed to hardness BHN 149 to 156). All tools except 7 were tested under the following conditions: 400 surface feet per minute (s.f.m.), feed:

feed. Compared with Carboloy 370 (a C-5 tool for roughing cuts), it gave a better finish up to a feed of 0.030 inch/ rev., but broken when the feed was raised to 0.040 inch/ rev. The data obtained with some of the alloys are shown in the accompanying drawing (FIG. 1) and the following table (Table 1).

TABLE 1 Test results At percent Sample MoNi or Time, Wear, designation Motco Sinter condition min. in. 1 12 100Cminutes at 1,490 90=02 0.00s 12 10%ininutes at 1,490 45:50 0. 001 5 hours at 800 0 12 90 minutes at, l,490 C. 45:37 0 006-0. 007 18 90 minutes at 1,500 C 31:40 0. 006 14 16 minutes at 1,500 O. 13:17 0.005 6 12 16 minutes at 1,500 G. 4:02 0. 003

7 15 80 minutes at. 1,490" 0. Variable feed Havingfully described the invention it is intended that it be limited only by the lawful scope of the appended claims.

I claim:

1. A novel titanium carbide cutting tool composition comprising TiC grains coated with a superimposed layer of a stoichiometric MoC, said coated grains embedded in a metal alloy binder matrix, said alloy binder containing a deficient amount of Mo and a rich portion of a binder alloy comember selected from the group consisting of Ni and Co, said binder alloy being derived from an intermetallic compound selected from the group consisting of MoNi and Mogco said composition'containing 13.6% to 30% by weight Mo wherein the composition comprises from about 50 to about w. percent TiC, the balance being MoC layer and binder matrix.

2. The titanium carbide cutting tool composition of claim 1 wherein the intermetallic compound is MoNi.

3. The titanium carbide cutting tool composition of claim 1 wherein the intermetallic compound is Mo Co 4. A novel method of preparing titanium carbide compositions containing at least 13.6 percent by weight molybdenum which comprises:

(1) ball milling titanium carbide with an intermetallic compound consisting of Mo Co (2) cold pressing the mixture,

(3) sintering the mixture at a temperature of at least References Cited UNITED STATES PATENTS 2,967,349 1/ 1961 Humenik, Jr. et al. 75-203 3,490,901 3/1970 Hachisuka 75-203 2,828,226 3/1958 Goetzel et a1. 75-203 2,752,666 7/1956 Goetzel et a1. 29-1827 2,711,009 6/1955 Redmond et al. 75-203 OTHER REFERENCES Shunk, Constitution of Binary Alloys, second supplement, 1969, McGraw-Hill, Inc., pp. 260-1, 515-7, TA490, H27aE.

CARL D. QUARFORTH, Primary Examiner B. HUNT, Assistant Examiner U.S. Cl. X.R. 75-203 

